1. Field of the Invention
The present invention relates to a receiving band switching circuit suitable for a television tuner or the like.
2. Description of the Related Art
FIG. 2 shows a related art receiving band switching circuit. A band pass filter (BPF) for FM 1 and a band pass filter (BPF) for TV 2 are provided between a front end and an antenna (ANT) for receiving a television signal and an FM broadcasting signal. The BPF for FM 1 is connected to the antenna through a diode D1, and is connected to the front end through a diode D2. The BPF for TV 2 is connected to the antenna through a diode D3, and is connected to the front end through a diode D4.
Cathodes of the diodes D1 and D3 are connected to the antenna, and are connected to a ground through a resistor R2. In addition, cathodes of the diodes D2 and D4 are connected to the front end, and are connected to a ground through a resistor R4. Anodes of the diodes D1 and D2 are connected to an FM terminal of a switch 3 through resistors R1 and R3, respectively, and anodes of the diodes D3 and D4 are connected to a TV terminal of the switch 3 through resistors R5 and R6, respectively.
Further, a voltage (+B) is applied between the FM terminal and the TV terminal, such that the diodes D3 and D4 or the diodes D1 and D2 are supplied with a current. The BPF for FM 1 or the BPF for TV 2 is switched, such that the FM broadcasting signal or television signal is switched and is inputted to the front end (for example, Japanese Unexamined Utility Model Registration Application Publication No. 63-64138 (FIG. 2)).
The resistors R2 and R4 are connected in parallel with the antenna and the front end, respectively, in order to cause the diodes D1 to D4 to be supplied with a current. However, in order to cause a current to flow in the diodes D1 to D4, it is impossible to increase the resistance values of the resistors R2 and R4. As a result, there is a problem in that the loss of a signal is increased.